This invention relates generally to overhead doors or curtains and is particularly directed to a lightweight roll-up door which can be lowered or raised at high speed.
Roll-type doors are frequently used in industrial installations to isolate two rooms or the inside of a building from the outside environment while permitting transit between the two rooms or either out of or into the building. Roll-up doors of the curtain type are generally secured at an upper end thereof to a tube-like roller which is rotated in a first direction to lower the door and in a second, opposite direction to retract the door. The roller is typically mounted immediately above the doorway and is generally rotationally displaced by an electric motor and drive assembly. Roll-type doors are generally comprised of a lightweight material to facilitate rapid displacement of the door and are also frequently transparent to allow for viewing through the doorway when the roll-type door is in the extended, closed position. These doors are typically comprised of a high strength plastic material such as polyvinyl chloride (PVC) and may be displaced from the open to the closed position, or vice versa, in just a few seconds. As this type of door lacks the structural strength of heavier multi-section hinged roll-type doors, these lightweight roll-type doors are intended primarily for environmentally isolating two adjacent rooms or the inside of a building from the outside environment rather than for providing security by preventing transit through a doorway. A rapidly displaced overhead roll-type door having good insulating characteristics is particularly desirable from an energy conservation standpoint where there is a large differential between inside and outside temperatures.
Pliable roll-type door tensioning arrangements typically include various combinations of springs, pulleys and weights to exert a downward force on the lower edge portion of the door in maintaining it generally planar across the doorway when extended. These arrangements in the past have tended to be overly complex and of limited reliability over extended periods of continued use. The present invention is intended to overcome the aforementioned limitations of the prior art by providing a high speed roll-type door which has a reduced number of parts while offering highly reliable performance.